JPH05194554A - Process for producing organosiloxane - Google Patents

Abstract

PURPOSE: To obtain organosiloxane of a low molecular group in a high proportion in particular and hydrochloric acid by hydrolyzing organosilane in the presence of methanol.

CONSTITUTION: Organochlorosilane is hydrolyzed at 40 to 90°C for 5 to 30 min in the presence of methanol to obtain organosiloxane contg. organosiloxane of low molecular weight of >75 wt.%, preferably, >85%. At the same time, gaseous hydrogen chloride is formed in a high proportion. The ratio of aq. phase water separated from an organosiloxane product in a phase separator : methanol is regulated to 0.3 to 10, and this organosiloxane is useful as the raw material for silicone.

COPYRIGHT: (C)1993,JPO

Description

Detailed Description of the Invention

The present invention prepares organosiloxanes, in particular organosiloxanes having low molecular weight cyclic and chain structures, preferably those containing a high proportion of cyclic dimethylsiloxane, by hydrolysis of the corresponding organochlorosilanes. At the same time, it relates to a method of generating gaseous hydrogen chloride at a high ratio.

Organosiloxanes are an important source of silicone chemistry. Organosiloxanes are generally obtained by hydrolysis of organochlorosilanes. Hydrolysis is carried out via an intermediate step to produce organic silanols and hydrogen chloride is separated. Under acidic conditions, the silanol group is extremely reactive and undergoes a secondary reaction with the SiCl or SiOH group, resulting in the characteristic siloxane group (Si-O-S) of silicone.
i) occurs. When using diorganodichlorosilane,
Cyclic diorganosiloxanes result from the formation of the α, ω-dihydroxypolydiorganosiloxanes with the chain structure used in the synthesis of high molecular weight organosiloxanes. Branched organosiloxanes result from the use of organotrichlorosilanes; triorganomonochlorosilanes give hexaorganodisiloxanes and mixed silanes give mixed forms of the above organosiloxanes.

Since organic siloxanes having a relatively high molecular weight have high viscosities, it is not desirable for them to be present in the subsequent steps such as purification and distillation. Thus, attempts to increase the proportion of low molecular weight organosiloxanes in the hydrolysis product have not previously been unsuccessful.

Thus, the content of cyclic products in the hydrolysis product can be increased to 95% by adding surfactants (US Pat. No. 3,983,148).
No. 4, 412 080, No. 4 423 24
No. 0, No. 4 447 630). However, these methods are unsatisfactory because the surfactant must be subsequently removed from the siloxane mixture. This is because a slight amount of impurities of about 1 ppm can be a cause of deterioration of the polyorganosiloxane later.

In another method for producing organosiloxane, organochlorosilane and methanol are used as raw materials for the purpose of obtaining organosiloxane and methyl chloride (methanol decomposition). In the Roshow synthesis method, methyl chloride is used directly to react with metallic silicon to form methylchlorosilane. However, the reaction of reacting the organic chlorosilane with methanol to form the organic siloxane and methyl chloride proceeds relatively slowly, so that an unsatisfactory volume / time yield is only obtained. Therefore, a catalyst for producing methyl chloride was also developed (German Patent A 25
No. 57 624), the yield is 3 to 4 times lower than the yield of the hydrolysis reaction, and no advantage is obtained as compared with the case where methyl chloride and siloxane are simultaneously produced. Further, in the case of methanol decomposition, an aqueous hydrogen chloride solution is always obtained, and this must be discarded.

The main object of the present invention is to provide a method which makes it possible to produce organosiloxanes containing more than 75% by weight, preferably more than 85% by weight, of low molecular weight organosiloxanes and avoids the disadvantages of the methanol decomposition process. It is to be.

From a process engineering point of view, the method according to the invention belongs to the type of method carried out using the apparatus shown in FIG. The technical arrangement of the method according to the invention will first be described with reference to FIG. First, the reagent is introduced into the hydrolysis reactor 1 through one or more pipes 2, 3, 4. A stirrer 15 for stirring the reagents is attached to the reactor 1. The liquid phase is transferred along the pipe 5 to the phase separator 6, in which the reaction liquid composed of two phases having different densities is separated into an upper phase and a lower phase. Hydrolysis products of organosiloxane are removed through pipe 7. The pipe 7 is connected to the phase separator 6 above the interface of the two phases, the hydrolysis products being transferred to the purification stage and from the lower phase separated in the phase separator still attached to it. The residue can be removed. The lower phase, which contains mainly all other components of the reaction liquid other than the hydrolysis products, is removed from the phase separator via pipe 8. This lower phase is either no further processed and is discharged from the process through pipe 9 or returned to the hydrolysis reactor through pipe 10. The gaseous hydrolysis products are removed above the hydrolysis reactor through pipe 12 and into reflux condenser 13 where condensable components are removed,
This component is returned to the hydrolysis reactor. The condensable component-free gaseous hydrolysis product is withdrawn from the reflux condenser along the pipe 14 for further use.

The process according to the invention also belongs to the class of processes in which organic chlorosilanes are converted into organosiloxanes in the presence of water, methyl alcohol and hydrochloric acid without the presence of catalysts which favor the formation of cyclic components.

In the present invention, it has been found that the hydrolysis product contains a particularly high proportion of low molecular weight organosiloxanes provided that methanol is maintained at a certain value in the reaction solution. In a general aspect of the process of the present invention, the lower phase separated in the phase separator and containing mainly water, hydrochloric acid and methanol contains water and methanol in a molar ratio of 0.3-10. This molar ratio is preferably greater than 0.6, most preferably greater than 0.9. The upper limit of this molar ratio is preferably 3, more preferably 1.8, and most preferably 1.2.
Is.

The raw material used in the present invention is in particular a diorganodichlorosilane, which gives a high proportion of cyclic diorganosiloxane. The preferred diorganodichlorosilane is dimethyldichlorosilane.

The invention is illustrated below using the example with dimethyldichlorosilane. Of course, this description also applies to the hydrolysis of other organosilanes.

Therefore, in the present invention, dimethyldichlorosilane, water and methanol are supplied through the pipes 2, 3 and 4 of FIG. 1, and the supply amount is such that the ratio of water to methanol of the liquid leaving the phase separator through the pipe 8 is equal to that of the liquid. It is adjusted to fall within the features of the present invention.

According to the invention, the average reaction time in the reactor is limited to less than 30 minutes. By average residence time is meant the total amount of reagents fed per hour through pipes 2, 3 and 4 divided by the volume of liquid in the hydrolysis reactor. Therefore, if the take-out pipe 5 of the hydrolysis reactor is arranged as an overflow pipe in the usual way, the height of the liquid in the hydrolysis reactor will be at the level of the mouth of the overflow pipe 5. is there.

According to the invention, the temperature in the hydrolysis reactor is maintained at 40-90 ° C. Temperatures up to 120 ° C. have no advantage with respect to the yield of cyclic organosiloxane,
Elevated temperatures up to 120 ° C. are advantageous for the production of methyl chloride, which is removed from the process through the pipe 14 along with the non-condensing gas components. But pipe 1
Increase the proportion of methyl chloride in the gaseous hydrolysis product if the gas mainly consisting of hydrogen chloride removed through 4 is then converted to methyl chloride for further use in Rocheau synthesis. It is desirable to reduce the amount of work in the reactor that is subsequently used in the reaction of hydrochloric acid with methanol to give methyl chloride. However, for process engineering reasons in the operation of the hydrolysis reactor it is preferred not to use excessively high temperatures. A temperature of 50-80 ° C. is particularly suitable as it is particularly suitable for degassing hydrogen chloride.

The hydrolysis reactor can be operated at normal gas pressure, but the process can also be carried out with a slight vacuum. However, slightly higher pressures are generally preferred. This is because this facilitates the transport of gaseous hydrolysis products through the pipe 14. When the method of the present invention is carried out on a large-scale industrial scale,
It is advantageous to use an overpressure of about 1 bar as it helps to transfer through pipe 14 to the next device without a pump. It is advantageous to further increase the pressure up to 2 bar in order to reduce the volume of bubbles in the hydrolyzate.

The liquid phase must be vigorously stirred in the reaction vessel. Various devices known in the art, such as a stirring vessel equipped with a powerful stirrer with a control plate, a column containing various attachments or packings, a static stirrer with an adjoining rest zone, etc., as a mixing device Can be used. Whatever the arrangement, it must be possible to carry out phase separation after the reaction both in the gas-liquid zone and in the oil, water and liquid zones.

When dimethyldichlorosilane is supplied in liquid form at room temperature, the temperature in the hydrolysis reactor can be adjusted by an external heating device, but also after the dimethyldichlorosilane is evaporated at high temperature, It is introduced into the bottom in gaseous form and can thus be used for temperature control. When dimethyldichlorosilane is supplied in the form of gas, it is introduced into the hydrolysis reactor in the form of sufficiently small bubbles, and the surface of the hydrolysis liquid discharged from the reactor together with the gaseous hydrolysis products. Care must be taken to prevent air bubbles from passing through. For process engineering reasons, dimethyldichlorosilane is introduced in liquid form below the liquid level,
Alternatively, it seems simplest to introduce it into the hydrolysis reactor by allowing it to fall freely into the gas space above the liquid level.

The reaction introduces the gaseous reactants into the gas space above the hydrolyzed liquid, the hydrolysis mainly taking place in the gas space, and the condensable products produced by the hydrolysis are reflux condensers. It is also possible to condense it in the reactor and return it to the hydrolysis reactor. Although this reaction method is not advantageous from the viewpoint of energy, it does not substantially require degassing from the volume of the liquid, resulting in a high volume / time yield.

In the present invention, water and methanol are also introduced into the hydrolysis reactor at a ratio of at least 1 mol per equivalent of chlorine directly bonded to silicon in the fed organochlorosilane to introduce the organochlorosilane. After removing 0.5 mol of water per equivalent of chlorine directly bound to silicon, the molar ratio of water and methanol fed is still 0.3 to 10, preferably 0.9 to 1.8. By doing so, the amount of methanol required for the present invention can be maintained in the lower phase removed from the phase reactor. According to this experimental finding, in the ideal case of the present invention, after removing 0.5 mol of water used in the hydrolysis reaction, the molar ratio of water to methanol was about 0.9 to 1.2. In some cases it seems optimal.

According to the invention, it is preferred to return the lower phase leaving the phase separator at least partially to the hydrolysis reactor. In this way, the amount of fresh water and methyl alcohol supplied can be reduced by the amount returned.

If the reactor is in the form of a simple stirred vessel, the volume of the reactor according to the invention (when filled with liquid)
At least about 8 organosiloxanes per liter per hour
It can be obtained in a yield of 00 g. The yield of cyclic dimethylsiloxane is at least 560 g / l of reactor volume (filled with liquid) per hour. Reaction volume 1
Up to 2000 g of organosiloxane are obtained per liter.

A limiting factor in volume / time yield is the separation of gaseous products from hydrolysis products. According to the present invention, the volume / time yield can be easily increased by a factor of 2 to 3 by using a reactor specially designed for the degassing step. However, according to the present invention, even if the optimum volume / time yield is not obtained, the technical investment cost is small, so that a simple enamel-lined stirring container is preferable.

According to one (particularly preferred) embodiment of the invention, it is possible to obtain substantially 100% of the hydrochloric acid theoretically obtained from dimethyldichlorosilane in the form of a gaseous hydrolysis product. .. In this particularly preferred embodiment of the invention, the lower phase obtained from the phase separator is returned to the 100% hydrolysis reactor, where the amount of water returned to the hydrolysis reactor is dimethyldichlorosilane silicon. Chlorine bound directly to
It should be only about 0.5 mol per equivalent. However, in practice, a slightly larger amount of water and a smaller amount of methanol must be supplied. . This is because the gaseous hydrogen chloride released still contains a small amount of methyl chloride, which has to make up for the amount of water and methanol lost with the released hydrolysis products. Therefore, in a particularly preferred step of the present invention, only 0.5-0.
Equivalent to methanol released by introducing 55 mol of water into the hydrolysis reactor, returning all the lower phase obtained in the phase separator, and circulating in the form of methyl chloride, and methanol attached to the upper phase. Add as much methanol as you want. Therefore, in the present invention, the circulating liquid in the lower phase of the hydrolysis reactor and the phase separator includes organic chlorosilane,
Only 0.5 to 0.55 mol of water per equivalent of chlorine directly bonded to the organochlorosilane, and 0.001 per equivalent of chlorine directly bonded to the silicon of the organochlorosilane.
Most preferably, only 0.1 mol, preferably up to 0.05 mol of methanol is fed.

According to the invention, methanol does not itself form a reaction product but participates in the reaction only as an intermediate. Clearly, in the present invention, methanol acts as a catalyst or catalyzed reaction medium that promotes the formation of cyclic products and low molecular weight organosiloxanes.

In this preferred method of the present invention, at least 75% of the theoretical yield from the resulting organochlorosilane is obtained as gaseous hydrogen chloride, and the yield of organosiloxane is determined by the reactor liquor fill. ) It can be increased to about 1200-2000 g / l volume.
The yield of cyclic dimethyl siloxane is at least 950 g / h / liter of the reactor (full of liquid). The steady state of the process of the invention is to introduce 3 parts water and 1 part methanol (on a molar basis) into the hydrolysis reactor,
This can then be achieved from the start of the reaction by feeding the amounts of organochlorosilane, water and methanol in the exact ratios given above so that the average residence time defined above is about 5 to 30 minutes.

Until equilibrium is reached, the rate of addition of methanol must be varied according to the analysis of the lower phase exiting the phase separator so that equilibrium in the continuous process can be achieved quickly.

The preferred embodiment of the process of the invention was tested over a long period of time and found that the product did not interfere with the process. No dimethyl ether was found to interfere with the process, except a small amount of methyl chloride was present in the gaseous hydrolysis product. This is probably due to the relatively high concentration of HCl in the hydrolysis reactor.

The water required for the process according to the invention can be supplied in the form of an aqueous hydrochloric acid solution. It may further contain components from the hydrolysis reactor for use in washing the hydrolysis products, for example less concentrated than the composition of the azeotrope, to remove the components attached to it from the lower phase of the phase separator. It is advantageous to supply fresh hydrochloric acid as the water required for the hydrolysis. At this time, the excess amount of hydrochloric acid introduced into the hydrolysis reactor can be obtained as an excess amount of gaseous hydrochloric acid. 120% of the amount of hydrogen chloride theoretically obtained from the organohalogenosilane used in the process in this way can be withdrawn from the process in the form of gaseous hydrogen chloride through the pipe 14 of FIG. That is, the hydrochloric acid aqueous solution in this proportion can be dehydrated to form gaseous hydrogen chloride.

High volume / time yields are obtained in the preferred process of the present invention, with about 80% cyclic dimethylchlorosilane.
From the viewpoint that the lower phase is quantitatively circulated from the phase separator and the chlorine can be quantitatively recovered in the form of gaseous hydrogen chloride, the methyl chloride can be simultaneously recovered in only one reactor. The technical efforts to obtain methanol decomposition favoring the formation of cyclic products on a profitable basis are the result of previous work which has hampered the discovery of the catalytic effect of methanol on hydrolysis. Methanol decomposition itself of organic chlorosilanes that accompanies the formation of methyl chloride is a process of releasing water, and it is inevitable that hydrochloric acid aqueous solution is generated, and it is not possible to easily find a good application for this.
At first, the knowledge that methanol could be present in the presence of methanol under certain conditions to favor hydrolysis without aiming to obtain a product with methanol deviated from the above-mentioned goal of technological development.

The invention is illustrated in detail by the following examples. However, these examples do not limit the general features of the invention.

[0031]

【Example】

Examples 1 to 5 The reaction vessel used was equipped with two powerful reflux condensers connected in series, a stirrer made of glass, a contact thermometer, and a short inlet tube with two inlets. It was a 4-liter four-necked flask. An overflow tube provided at half the height of the flask (volume of liquid 1 liter) went through a submerged feed pipe below the liquid level to a 0.5 liter horizontally placed separation flask. The flask is equipped with a lower phase take-off tube and an upper phase take-out tube. The contact thermometer is relayed to a heating mantle that covers the bottom half of the flask. A powerful water-cooled reflux condenser was connected to a 2-liter two-necked flask by a gas discharge pipe, and one column was equipped with a column packed with a packing material having a length of 80 cm and a diameter of 3 cm. Water is dripped from above into the column packed with this packing material, and the generated gas is absorbed. Water is 1
It can flow from the bottom of a liter flask to a receiver via a subsurface feed pipe. The type and amount of gas produced is thus determined in the aqueous phase. The top of the column is evacuated by a tube with two wash bottles for safety. Each of the two inlets on the short inlet tube of the reaction vessel is connected to a laboratory metering pump via a Teflon tube. The inlet side of each pump is connected to a storage container for dimethyldichlorosilane or a hydrochloric acid / methanol / water mixture via a Teflon tube having an intake suction tube.

First, the amount of methanol shown in Table 1 was added to the reactor /
Fill with water or a methanol / hydrochloric acid / water mixture. This mixture and dimethyldichlorosilane are then added in the amounts shown in Table 1. The temperature shown in Table 1 is kept constant. Equilibrium is reached after about 2 hours.

The upper phase was washed immediately after coming out, and then 2%
Mix with sodium hydroxide solution. After separating the sodium hydroxide solution, the viscosity of the silicone oil was determined as shown in Table 2. In the last column from the end of Table 2, the yield in g of cyclic dimethylsiloxane (n = 3 to 8) per liter of reaction volume (volume filled with liquid) per hour, and The overall yield of silicone oil was shown. The table also gives the analytical values of the gaseous product stream, the hydrochloric acid content of the lower and upper phases, in units of g / h (upper number) and mol / h (lower number).

[0034]

[Table 1]

[0035]

[Table 2]

Example 6 The same equipment was used as in Examples 1-5, but the lower phase leaving the separation flask was returned directly to the reactor. 3 to start the reaction
00 g methanol, 300 g HCl and 300 g
H ₂ O mixture is introduced. 2220 g of dimethyldichlorosilane (17 mol) per hour, 310 g of water (17.
2 mol) and an average of 27 g of methanol (0.85 mol) were introduced continuously. Keep the reactor temperature at 58 ° C. After 2 hours certain conditions were established.

1300 g of liquid per hour were separated as the upper phase. This liquid contained 45 g of hydrochloric acid and 1250 g of silicone having a viscosity of 6.0 mPa sec. The proportion of cyclic silicone was 84.5%. The gas phase is 1665 which corresponds to 94% of the amount theoretically obtained from dimethyldichlorosilane.
It contained g HCl gas (32 mol), and 40 g methyl chloride. After continuous operation for 10 days, the reaction was stopped without any trouble.

Example 7 The procedure was the same as in Example 6, but instead of water, 390 g of 20% hydrochloric acid obtained by washing the silicone product were fed. Otherwise the product data were essentially unchanged, and the resulting gas phase contained 1245 g of HCl gas (34 mol).

The main features and aspects of the present invention are as follows. 1. A method of producing organic siloxane and hydrochloric acid by hydrolyzing an organic chlorosilane in a hydrolysis reactor and separating a product organic siloxane from a hydrolysis liquid by phase separation, to perform hydrolysis in the presence of methanol.

2. The aqueous phase separated from the organosiloxane product in the phase separator has a water to methanol ratio of 0.3 to 1
The method according to claim 1, wherein the method is 0.

3. After feeding the organochlorosilane, water and methyl alcohol to the hydrolysis reactor and removing 0.5 mol of water per equivalent of silicon-bonded chlorine of the introduced organochlorosilane, the ratio of fed water to methanol is A method according to claim 1, wherein the value of 0.3 to 10 is still maintained in the reaction mixture.

4. The first to third additions of water and methyl alcohol in a total amount of at least 1 mol per equivalent of silicon-bonded chlorine of the introduced organochlorosilane.
Method described in section.

5. At least 1.1 in total per equivalent of silicon-bonded chlorine in the introduced organochlorosilane.
The method according to any one of claims 1 to 4, wherein water and methyl alcohol are added in an amount of 5 mol or less.

6. The method according to any one of the above items 1 to 5, wherein the lower phase obtained by separating the organosiloxane product is returned to the hydrolysis reactor.

7. In addition to the lower phase returned to the hydrolysis reactor, 0.5 to 0.55 mol of water and 0.001 to 0.1 per equivalent of silicon-bonded chlorine of the organochlorosilane.
The method of claim 6 wherein the moles of methyl alcohol are provided.

8. The method according to claim 7, wherein water is supplied in the form of an aqueous hydrochloric acid solution.

9. Average residence time in hydrolysis reactor is 5
The method according to any one of items 1 to 8 above, which is -30 minutes.

[Brief description of drawings]

FIG. 1 shows a flow chart of the method according to the invention.

Claims (1)

[Claims] 1. A method for producing an organic siloxane and hydrochloric acid by hydrolyzing an organic chlorosilane in a hydrolysis reactor and separating a product organic siloxane by phase separation from a hydrolysis liquid to produce an organic siloxane and hydrochloric acid. A method of performing.